The present invention relates to an ink jet recording head which records images by means of ejecting ink onto a piece of recording medium, and also to an ink jet recording apparatus comprising such an ink jet recording head. In this case, the terminology xe2x80x9crecordxe2x80x9d means to xe2x80x9capplyxe2x80x9d the ink or the like to any ink receptive medium which includes fabric, yarn, paper, sheet material of various types, and the xe2x80x9crecording apparatusxe2x80x9d means an information processing apparatus itself inclusive of printer, or the printer itself as the output device, to which the present invention is applicable.
Among various types of presently known recording systems, the ink jet recording system has been recognized as an extremely effective recording system, since it is a non-impact recording system which generates little noise during recording; it is capable of recording at a high speed; and in addition, it is capable of recording on plain paper without requiring a special fixing process.
FIGS. 15 and 16 illustrate the essential portions of a typical ink jet recording head employed in such an ink jet recording system. FIG. 15 is a schematic perspective view thereof, and FIG. 16 is an exploded perspective view thereof. FIG. 17 is a schematic sectional view of the internal structure of the ink jet recording head, at sectional plane Xxe2x80x94X.
Reference numeral 100 designates a base plate, on which various components (which will be described later) are constructed. On this base plate 100, a piece of substrate 200 (hereinafter, a heater board) is disposed, which comprises a plurality of electrothermal transducers (heaters) 201 as elements for ejection energy. On this heater board 200, an ink path (not. illustrated) leading to a plurality of ink ejecting orifices 301 is located, and also, to a predetermined point thereof, a top plate 300 is joined. The top plate 300 comprises: an orifice plate 304 with the ink ejection orifices 301; a common liquid chamber 302 for storing the ink to be supplied through the aforementioned ink path; and a cylindrical ink inlet pipe for supplying the ink to this common liquid chamber 302. The top plate 300 is joined with the heater board 200 in the following manner. First, the top plate 300 is temporarily glued onto the heater board 200, in such a manner that the plurality of heaters 201 of the heater board 200 become aligned with the correspondent ink ejection orifices 301 of the top plate 300, and then, a mechanical pressure is applied, from above, to the top plate 300, with the use of a spring (unillustrated), so that two components can be satisfactorily joined in an airtight manner. Thereafter, the peripheries of the top plate 300 and heater board 200 are sealed with sealant 400 as shown in FIG. 17, whereby the ink path and common liquid chamber 302 are airtightly sealed.
It is well-known that liquid chamber partitioning walls 303 are disposed on the heater board 200 so as to form the common liquid chamber 302 on the inward facing surface of the heater board 200 (Japanese Laid-Open Patent Application No. 101,958/1991, or the like).
Recently, however, the size of the heater board has been progressively reduced in order to reduce the size of the ink jet recording head as well as the heater board cost. As the results of this size reduction, there have been cases in which it is difficult, in terms of space, to form the liquid chamber walls on the inward facing surface of the heater board in a conventional manner. In addition, the reduced size of the heater board results in a reduced distance between the heater board edge and the outermost ink ejection orifice, and as a result, the sealant for sealing the common liquid chamber is liable to flow sometimes into the ink ejection orifices, creating thereby such a problem that the ink cannot be ejected.
Accordingly, the primary object of the present invention is to provide a highly reliable ink jet recording head, which is even smaller in size and cost, and in which the sealant does not flow into the ink path, and also to provide an ink jet recording apparatus comprising such an ink jet recording head.
According to an aspect of the present invention, the top plate overhangs from the edges of the substrate in the direction of the joint between the top plate and substrate; therefore, the size of the substrate can be reduced compared to the conventional one. In addition, the joint becomes smaller than the conventional one; therefore, it is less probable that gaps will occur between the top plate and substrate due to the microscopic surface irregularities that are present in the joint. Consequently, the airtightness of the joint between the top plate and substrate is improved, preventing the sealant from flowing into the ink path. Further, since the top plate is disposed in such a manner as to overhang from the joint, the thickness of the top plate wall members that form the ink path is allowed to be substantially the same as those of the conventional design; therefore, their strength can be maintained at substantially the same level as the conventional one.
According to another aspect of the present invention, the overhanging portions of the top plate are extended in the thickness direction of the substrate, and the substrate is disposed between the two extended overhanging portions; therefore, the sealant can be more reliably prevented from flowing into the ink path. Further, the extended portions of the top plate embrace the substrate; therefore, the strength, or reliability, of the ink jet recording head itself is improved.
According to another aspect of the present invention, a portion of one of the common changer walls projects toward the element substrate, the wall being the one that opposes the orifice plate. This projecting portion causes the mechanical pressure, which is applied to the top plate as the top plate and element substrate are joined, to be concentrated toward the ink path wall side of the element substrate; therefore, the ink path walls of the top plate, and substrate, can be airtightly joined with more reliability. Consequently, the sealant for sealing the joint between the element substrate and top plate can be reliably prevented from flowing into the common liquid chamber and/or ink ejection orifices.
According to another aspect of the present invention, a part of the extended overhang portion of the liquid chamber wall is cut away; therefore, the adhesive used to join temporarily the top plate and element substrate can be reliably prevented from flowing into the ink path.
According to a further aspect of the present invention, notches are cut in the extended overhang portion of the liquid chamber wall; therefore, the surface area, which comes in contact with the adhesive used for joining temporarily the top plate and element substrate, can be increased, whereby the adhesive strength is improved.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.